The present invention relates to a mechanism and a method for feeding a sheet from a sheet cassette in an image recording apparatus such as a copying machine, and more particularly to a mechanism and a method of feeding a developer sheet from a sheet cassette in an image forming machine which employs a photosensitive pressure-sensitive recording sheet for carrying a latent image thereon and transferring a developed image to the developer sheet.
In general, image recording apparatuses such as the copying machines employ continuous photosensitive recording mediums such as microcapsule sheets and developer sheets used in combination with the photosensitive recording mediums. Developer sheets are stacked in a sheet cassette and usually fed one at a time from the sheet cassette by a semicircular separator roller of rubber. The separator roller and the developer sheets have different coefficients of friction. The separator roller frictionally separates the uppermost developer sheet from the lower stack of developer sheets, and delivers the separated developer sheet to a certain position.
If the developer sheets are stacked such that their reverse sides face up, then the separator roller contacts the reverse side of the uppermost developer sheet. Therefore, when the uppermost developer sheet is fed out of the sheet cassette, the color developer layer on the uppermost developer sheet rubs against the reverse side of the next developer sheet, and the developer material tends to be partly peeled off from the developer sheet. Thus, an image formed on the developer sheet may be damaged where the developer layer has been removed, resulting in poor image quality.
If the developer sheets are stacked such that their developer layers face up, then the separator roller contacts the developer layer on the uppermost developer sheet. Therefore, when the uppermost developer sheet is fed out of the sheet cassette, the separator roller tends to slip on the color layer, which may be partly peeled off. Accordingly, an image on the developer sheet may also be impaired.
Japanese Laid-Open Patent Publication No. 55-93744, for example, discloses a sheet feed mechanism which does not employ a frictional separator roller but uses a suction cup for attracting a sheet under a vacuum and feeding the attracted sheet to a certain position. According to the disclosed sheet feed mechanism, if the vacuum is too intensive, the uppermost sheet attracted by the suction cup also attracts the lower sheet or sheets under suction, and hence more than one sheet may be fed out simultaneously. The lower sheet or sheets may also be attracted to and fed with the uppermost sheet due to static electricity developed between sheets. In order to separate sheets from each other, air is ejected between them. If the vacuum is too small, the attracted sheet may drop off the suction cup due to the applied air. The sheet feed mechanism includes a support base for placing a stack of sheets which is movable up and down. Therefore, the sheet feed mechanism is relatively complex and requires a large amount of energy to be consumed. Another problem is that some stacked sheets are liable to be scattered by the applied air jet. When the support base is lowered with the uppermost sheet attracted by the suction cup, tho suction cup is moved laterally so that the leading end of the sheet can be nipped by a feed roller and a pinch roller. While the suction cup is being moved laterally, however, the attracted sheet may be dropped off from the suction cup. Therefore, the disclosed sheet feed mechanism does not operate highly reliably.